would 87 octane be a better gas to get to receive better gas mileage in my 99 GT coupe or 93? thanks ........

Mike Jung

05-27-2005, 10:29 AM

would 87 octane be a better gas to get to receive better gas mileage in my 99 GT coupe or 93? thanks ........

What ever grade that has the most energy content in the gasoline.

Each brand could be different.

I know that Sunoco here in Southern-Ontario, advertises that the Ultra 94 has the most energy content in it's own brand of gasoline (that is blended with up to 10% ethanol).

Note: Make sure you use a minimum of 87 octane (or 89 octane, if blended with up to 10% ethanol).

& "...It is important to note that the theoretical energy content of gasoline when burned in air is only related to the hydrogen and carbon contents.
The energy is released when the hydrogen and carbon are oxidised (burnt), to form water and carbon dioxide.
Octane rating is NOT fundamentally related to the energy content, and the actual hydrocarbon and oxygenate components used in the gasoline will determine both the energy release and the antiknock rating..." from: http://www.repairfaq.org/filipg/AUTO/F_Gasoline2.html#GASOLINE_004

& ethanol blended gasoline will get you a little worse mileage (less energy content); but it burns cleaner (more oxygen content) by running leaner.
According to a '98 C5 LS1 owner: ethanol blended gas will mess-up the timing (retards timing) for max performance in a high performance car. Seen via a scan tool.

rckrzy1

05-27-2005, 10:33 AM

I find you get roughly 10% better milage between 87 and 93 so if the cost is less than
10% more get the 93 .

Hodge

05-27-2005, 10:36 AM

is it the same for 2.4L's?

tenspeed

05-27-2005, 11:21 AM

Run two or three tanks full and keep track of your miles per gallon, not miles per tank. If the MPG is the same, buy cheap. If the MPG is better with the 93, buy it at any price, your engine is more effecient using it.

My wife did this with our Chevy van and found the more expensive gas cost less per mile than the less expensive gas.

Pontiac Ninja

05-27-2005, 11:26 AM

I had heard that using the higher octane (93 or 91) in our cars could be bad because its not made to run on gasoline that high. Only if you have the DHP or something, is when you should get 91. I know I read a thread where ppl were talking about this b4.

DarkPhoenix

05-27-2005, 12:24 PM

I did a test like that with my gfs GT and hers got better economy and performance out of the 87 than it did with the 93. The percentage of economy was only about 5 percent (20mpg city w/87 vs 19mpg City w/93) But her car ran better with the 87.

sc02grandam

05-27-2005, 03:36 PM

93 wont help gas milleage on a stock car

in fact i think you'll get lower gas milleage

Panacea

05-27-2005, 05:01 PM

I find you get roughly 10% better milage between 87 and 93 so if the cost is less than
10% more get the 93 .

I'd like to see the way you figured that out. Unless you took two, brand new, identical engines and ran them side by side at the exact same RPM, I would believe you. But since that's not the case, I don't.

Panacea

05-27-2005, 05:03 PM

I did a test like that with my gfs GT and hers got better economy and performance out of the 87 than it did with the 93. The percentage of economy was only about 5 percent (20mpg city w/87 vs 19mpg City w/93) But her car ran better with the 87.

There are way too many factors contributing to why you may get better gas milage with one or the other. Running 93 octane could have cleaned the fuel injectors out and caused the better mileage. Unless you take several hundred tanks and compare them, you can't come up with an accurate answer.

w82drv

05-28-2005, 10:55 AM

well im tryin this out where im gonna buy 3 tanks of 87 and do an oil change and than 3 tanks of 93. u might ask yourself why im doin this, well bc i wana know lol

Molson

05-28-2005, 12:10 PM

my 89 Shadow run on 98 and sometimes 110 weekly. :D

BigTaters

05-28-2005, 03:56 PM

oki will put an end to this.. as i worked for GM and Esso in my life lol..

supreme 91, 92, 9o3, 94 octane is better if the car is aging and up there in km/miles .. it will add fuel economy and it is proven to in aging cars.. if it is a newer car like ours with a moderate amount of power it wont help much at all actually.. unless u have mods done or high kms..

the other thing is mohawk and other places with ethanol gas .. sure it is 94 octane but ethanol is harder on the engine than regular gas is..

so ya unless your car is modded or higher on km/miles 87 octane is just as good for ya..

but i did do a test with my older camaro with a 350 in it a few years back and i could get about an extra 60 km outta a tank of gas when i used 93 octane instead of 87 so it does work.. alot of people with older cars used it.. especially old muscle cars. and they would add octane boost to it as well

Panacea

05-28-2005, 04:21 PM

oki will put an end to this.. as i worked for GM and Esso in my life lol..

supreme 91, 92, 9o3, 94 octane is better if the car is aging and up there in km/miles .. it will add fuel economy and it is proven to in aging cars.. if it is a newer car like ours with a moderate amount of power it wont help much at all actually.. unless u have mods done or high kms..

the other thing is mohawk and other places with ethanol gas .. sure it is 94 octane but ethanol is harder on the engine than regular gas is..

so ya unless your car is modded or higher on km/miles 87 octane is just as good for ya..

but i did do a test with my older camaro with a 350 in it a few years back and i could get about an extra 60 km outta a tank of gas when i used 93 octane instead of 87 so it does work.. alot of people with older cars used it.. especially old muscle cars. and they would add octane boost to it as well

Did you ever think that higher octane has more detergents in it and could possibly be cleaning out the various components, in turn increasing fuel economy? That's what it sounds like to me, so if you maintain your car properly, the need for a higher octane is unecessary.

BigTaters

05-28-2005, 07:02 PM

well dude it dont matter wtf kinda maintenance u do over a 10 year period if u bag on your car from time to time which everyone does and some do more than others and put 180,000 km on it the damn thing isnt going to run like the day you bought it.. lets be realistic here.

if you just run like one tank of supreme or maybe 2 you arent goin to notice it much.. but if you run it over and over you will notice the car runs better and is more fuel efficient(older and high mileage autos i mean)

Breadfan

05-28-2005, 10:24 PM

oki will put an end to this.. as i worked for GM and Esso in my life lol..

supreme 91, 92, 9o3, 94 octane is better if the car is aging and up there in km/miles .. it will add fuel economy and it is proven to in aging cars.. if it is a newer car like ours with a moderate amount of power it wont help much at all actually.. unless u have mods done or high kms..

Supreme works better on older cars due to a few factors involving buildup -

1.) Extra detergents - cleans injectors, valves, etc.

2.) Carbon build up on pisons and combustion chambers can actullay INCREASE compression ratio as a car ages.

In our cars you won't see much of an improvement over 87 octane. The higher the octane the less the gas will burn -- this is required in high compression engines or other apps where higher heat is involved. Higher octane helps prevent detonation on these cars. Our cars under normal circumstances don't require higher octane.

It's funny, people think "high octane" is so great all the time...it's only great if you're engine is designed to use it. I saw a show today on TV and they were showing a video of someone lighting a fire with gasoline. They were hyping it up and making it more dramatic saying it was "high octane gasoline". Like that was supposed to make it more dangerous. :) In fact, your 87 octane is gonna ignite before your 93 octane. ;)

Now on some cars designed for 87 octane you can get better efficiency with 91/93 octane simply becuase their PCMs and knock sensors are smart enough that they will actually keep timing advanced further since the higher octane will not detonate as early as the lower octane. Simpler PCMs only retard timing when knock is detected.

atc3434

05-28-2005, 11:41 PM

From what I've seen scanning, I pull more timing and less injector pulse width with the higher octane on the highway. The car actually has two different spark curve maps that it relies on for ignition timing, and will use less timing with less octane, to prevent dentonation. This holds true for full throttle output as well as cruising. Also, the car tends to use a bit more injection pulsewidth with the junkier gas. So, the car get better mpg with higher octane. I can't say its enough to offset the price, but I like no knock retard and better timing when my foot welds itself to the floorboard periodically.

Mike Jung

05-29-2005, 10:08 AM

is it the same for 2.4L's?
Yes.

From what I've seen scanning, I pull more timing and less injector pulse width with the higher octane on the highway. The car actually has two different spark curve maps that it relies on for ignition timing, and will use less timing with less octane, to prevent dentonation. This holds true for full throttle output as well as cruising. Also, the car tends to use a bit more injection pulsewidth with the junkier gas. So, the car get better mpg with higher octane. I can't say its enough to offset the price, but I like no knock retard and better timing when my foot welds itself to the floorboard periodically.

Atc3434,

Can you confirm (via scanning):

That the GA (stock or modified) in the summer, when the engine is running hotter.
'Pulls/retards timing' or picks-up more 'knock' (vs when the engine is running cooler at the 'normal' temperature range).

IIRC, I heard others say that our GA's WILL pull/retard timing or pick-up more knock, when the engine is running hotter in the summer.
& when the engine is hotter, that the engine runs more leanly.

So even if our minimum requirements are 87 octane; there are times that it WOULD benefit from a little higher octane.
(example: With blended up to 10% ethanol gasoline)

Regading: Octane vs Gas Mileage.
Also did no one read what I posted earlier; about gasoline energy content; & that it is independant of octane rating.

Offtopic:
By the way...

IIRC (I don't remember the exact #'s), I did about just over 800km [500miles] using about 60L [15.85US Gallons] on a highway trip from Toronto to Quebec City in the winter time around Christmas/New Years using cruise control @ 120km/h [74.6mph]
Both ways it was relatively the same.
I do remember the mpg was about 33mp(US)g.

I repeated that range of mpg (both ways) in the late spring to Ottawa on a highway trip using the cruise control.

When my car was new/stock using gasoline from Esso 92 octane & Sunoco 94 octane (that is blended with up to 10% ethanol).

atc3434

05-29-2005, 11:24 AM

Atc3434,

Can you confirm (via scanning):

That the GA (stock or modified) in the summer, when the engine is running hotter.
'Pulls/retards timing' or picks-up more 'knock' (vs when the engine is running cooler at the 'normal' temperature range).

IIRC, I heard others say that our GA's WILL pull/retard timing or pick-up more knock, when the engine is running hotter in the summer.
& when the engine is hotter, that the engine runs more leanly.

So even if our minimum requirements are 87 octane; there are times that it WOULD benefit from a little higher octane.
(example: With blended up to 10% ethanol gasoline)

The computer has a table which will retard timing when the intake air temperature reaches a certain temperature. If the air is hot, it will pre-ignite much easier. Also, a hot engine is much more likely to exerience pre-ignition, thats much of the reason for people running a 180* thermostats. Higher octane gas limits this tendency for pre-ignition, so you can pull more timing without spark knock.

I've noticed that when highway cruising, the engine is more likely to knock. This is probably due to very hot compustion chambers, from the car running lean mixtures to maximize fuel economy. 93 octane is a benifit, but I don't know if it saves enough fuel to offset the cost for the higher price.

R8DERHED5150

05-30-2005, 06:05 PM

In a stock vehilcle, especially these new ones, high octane don't mean a thing unless you are running a turbo/supercharger. Putting some high test in your ride is just a waste of money if its designed to run on 87. I've tried using all the grades available and never noticed any difference. My 99 GAGT has now become my commute car. My commute is 10 miles each way, with no traffic what soever, inturn giving me a consistant drive each time. I use whatever gas is cheapest at the time since the gas gods can never make up their mind how high they want to raise the prices. The only time I notice a change in milage is when its either hot or cold (we only have two seasons here, summer and winter). And I doubt they put more detergents in high test. I think that would degrade its combustability. So unless your car is PINGing, don't waste your money. But if you need that piece of mind that the extra 10 bux a tank will help, more power to you.